I fail to see how a sign indicating that one would be trespassing and liable to prosecution if they climbed the hill counter-productive at all. What it needs is the culprits to be actually brought to book instead of everybody just mamby-pambying around them all the time. WHY is nobody being prosecuted?

You're thinking from the perspective of someone who is responsive to reasonable requests. There are plenty of people out there with a contrary nature who will react to a reasonable request by doing the exact opposite.

I'm not sure HOW you expect prosecutions to take place? How will culprits be arrested, identified, and sufficient evidence gathered for a conviction?